The present invention relates to updatable photoplastic film recording and display devices and more particularly to a system to safeguard against double exposure of any frame on a microfilm or microfiche.
Microfilm recording is a process wherein photographically reduced images of objects, generally documents, are sequentially formed and recorded in successive frames on a reel of microfilm or on distinct frames of a fiche. Typically, a fiche conforms to standards set forth by the National Microfilm Association and contains ninety-eight frames, each having a particular size and location with respect to the overall fiche. One type of fiche in use today includes a photoplastic film which is updatable, that is, in which a frame containing a first recorded image may record a second new image thereover. When that happens, the first recorded image is lost or the frame is double exposed. While systems using updatable film have the advantage of recording over unwanted data, they are correspondingly subject to accidental recording over images which should be preserved.
One system which treats this problem is disclosed in "Photoplastic Film Recording and Monitoring Apparatus", U.S. Ser. No. 873,932 filed Jan. 31, 1978 by Gordon Lysle and Kenneth R. Baur, assigned to Bell & Howell, now abandoned. According to one embodiment of a photoplastic displays any document image which may have been previously recorded in the frame selected by a user for recording a (further) document. Thus, a manual inspection is necessary for each frame to insure against double exposures or accidental erasure.
A second embodiment described therein includes blank or occupied based on the surface alterations of the frame upon document recording. Briefly, a surface-viewing sensor unit is mounted on a shutter above the recording station. The sensor unit contains a small light source and a light sensitive diode. The sensor light is projected onto the frame and is reflected upwardly thereby. If the fiche is perfectly flat, the reflection will be detected by the light sensing diode and will release a control system for permitting recording. If, however, the frame is occupied by a recorded image, the film will have a bowed configuration or distortion which will deflect the light away from the sensor diode. The failure to receive a return signal by the sensor actuates an interlock system which prevents a recordation cycle when a RECORD command is entered by the user.
However, when a user erased a previously recorded document image so that a subsequent document image could be recorded, the erasure occasionally left some ripples in the photoplastic film surface. Those ripples caused the sensor unit to interpret the erased frame as an occupied image was automatically inhibited.
Accordingly, the principal object of the present invention is to provide a more reliable detection system for a photorecorder to detect whether a frame aligned in the recording station of the recorder already contains an image, and if so, to inhibit the recorder from recording